The introduction of a KF post-deposition treatment (KF PDT) of Cu(In,Ga)Se 2 (CIGS) thin films has led to the achievement of several consecutive new world record efficiencies up to 21.7% for the CIGS solar cell technology. The beneficial effect of the KF PDT on the photovoltaic parameters was observed by several groups in spite of differing growth methods of the CIGS layer. For CIGS evaporated at lower temperature on alkali-free, flexible plastic substrates, a postdeposition treatment to add Na was already successfully applied. However with the introduction of additional KF under comparable conditions, distinctly different influences on the final absorber alkali content as well as surface properties are observed. In this work we discuss in more details the intrinsically different role of both alkali-treatments by combining several microstructural and compositional analysis methods. The ion exchange of Na by K in the bulk of the absorber is carefully analyzed, and further evidences for the formation of a K-containing layer on the CIGS surface with increased surface reactivity are given. These results shall serve as a basis for the further understanding of the effects of alkali PDT on CIGS and help identifying research needs to achieve even higher efficiencies.
The experimental setup and results of the first search for invisible decays of orthopositronium (o-Ps) confined in a vacuum cavity are reported. No evidence of invisible decays at a level Brðo-Ps → invisibleÞ < 5.9 × 10 −4 (90% C.L.) was found. This decay channel is predicted in hidden sector models such as the mirror matter (MM), which could be a candidate for dark matter. Analyzed within the MM context, this result provides an upper limit on the kinetic mixing strength between ordinary and mirror photons of ε < 3.1 × 10 −7 (90% C.L.). This limit was obtained for the first time in vacuum free of systematic effects due to collisions with matter.
We report a new measurement of the n ¼ 2 Lamb shift in Muonium. Our result of 1047.2ð2.3Þ stat ð1.1Þ syst MHz comprises an order of magnitude improvement upon the previous best measurement. This value matches the theoretical calculation within 1 standard deviation allowing us to set limits on Lorentz and CPT violation in the muonic sector, as well as on new physics coupled to muons and electrons which could provide an explanation of the muon g − 2 anomaly.
Precision spectroscopy of the Muonium Lamb shift and fine structure requires a robust source of 2S Muonium. To date, the beam-foil technique is the only demonstrated method for creating such a beam in vacuum. Previous experiments using this technique were statistics limited, and new measurements would benefit tremendously from the efficient 2S production at a low energy muon (< 20 keV) facility. Such a source of abundant low energy μ + has only become available in recent years, e.g. at the Low-Energy Muon beamline at the Paul Scherrer Institute. Using this source, we report on the successful creation of an intense, directed beam of metastable Muonium. We find that even though the theoretical Muonium fraction is maximal in the low energy range of 2-5 keV, scattering by the foil and transport characteristics of the beamline favor slightly higher μ + energies of 7-10 keV. We estimate that an event detection rate of a few events per second for a future Lamb shift measurement is feasible, enabling an increase in precision by two orders of magnitude over previous determinations.
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